This invention relates to an improved respirator speech unit for a light-type respirator.
Light-type respirators are used by military and civilian organizations to shield a wearer's face and control the air supply, thus providing protection against toxic or noxious gases or other substance in the air. The type most commonly used has a rubber shell which fits over the wearer's face with the wearer drawing in purified air through a canister filter and exhaling to the atmosphere through an outlet control mechanism. As well, such a mask has a respirator speech unit containing a speech transmitter disc with a diaphragm, often of Mylar (trade mark) film so that the wearer's voice can be passed to the outside and the wearer can consequently communicate with others.
The outlet control mechanism of such a mask is usually associated with the respirator speech unit. A peripheral air passage is provided between the frame of the speech unit and the periphery of the speech transmitter disc, which passage is blocked when the wearer is not exhaling by a flexible annular valve positioned externally to the speech transmitter disc within the speech unit. The valve seals off the passage against flow of air from outside the mask but opens to permit flow of air from within the mask to the outside when the wearer exhales. The outward motion of expelled air when the wearer is exhaling prevents return flow reversion while this valve is open.
There have been several problems associated with the use of such gas masks. The speech transmitter disc in these units is centrally positioned in a cylindrical frame by screwing a support in which it is held into a corresponding receptacle in the closed end of the frame. To screw this support into the frame, the valve must be in position between the frame and this support. Consequently, unless care is taken when inserting the speech transmitter disc, the twisting action on the support may be transmitted to the valve and cause distortion or tearing of the valve and/or uneven compression because of tightening tolerances. In practice, therefore, maintenance of gas masks and fitting of the parts of the respirator speech unit together is done not by troops or men in the field, but by qualified and skilled expert technicians. Moreover, it is difficult and time consuming to clean or free the valve from foreign material as disassembly is necessary. This cannot be accomplished in the field and protection is lost until the mask is serviced or replaced. When a valve is in place in a respirator speech unit, it is not convenient to do day-to-day checks to ensure that the valve is operating properly or has not deteriorated to the point that it should be replaced. The mask must instead periodically or as required be returned to expert technicians to be overhauled.
Yet another problem with such respirator speech units is that because the valve is a relatively large flexible ring exposed to the atmosphere, dust readily accumulates on the valve and frequently prevents it from completely or effectively providing a seal when the wearer is not exhaling. This problem can produce serious consequencies for a wearer if it arises in the field; on a day-to-day basis, this problem requires regular maintenance by expert technicians even when the mask is not in use.
The outlet valve/speech unit now used has no provision for free breathing while the gas mask is being worn while harmful gas is absent, so the wearer becomes fatigued unnecessarily from the resistance caused by the canister and outlet valve to respiration. Additionally, in such a case, the canister becomes contaminated with dust and other impurities while its protection is not required.
Speech transmission qualities of such known respirator speech units are not high, speech vibrations being channelled through a reducing-diameter cone to the atmosphere so that there is a consequent reduction in sound propagation and some distortion as a result.
It is an object of the present invention to provide an improved respirator speech unit which will overcome or assist in reducing the above mentioned problems and difficulties of the known unit. It is a further object of the present invention to provide a construction of respirator unit which may additionally be provided with a means to allow free in/out air flow when there is no contamination nearby, while the mask is worn, which air flow could be immediately cancelled to provide filtration and prevent entry of outside air into the mask.